(1) Field of the Invention
The present invention relates to an oxygen-permeable, machinable, dimensionally stable, wettable, solvent-resistant, hard contact lens material consisting of a polymer formed by free radical polymerization to provide extended duration wearing capabilities.
(2) Description of the Prior Art
The prior art teaches the use of many different polymeric materials in contact lenses.
Poly-methylmethacrylate is highly advantageous in its excellent optical properties and durability, but it is relatively impermeable to oxygen.
The hydrogel materials consisting of polymers of 2-hydroxy ethyl methacrylate or N-vinyl-2-pyrrolidone are soft and have good wettability, but they have extremely poor mechanical strength, so that they are less durable and extremely difficult to handle. In addition, they provide an environment which is favorable for bacterial growth.
Silicone rubber is soft, resilient and highly permeable to oxygen, however this material is hydrophobic.
In the last few years, considerable attention has been directed to obtaining oxygen permeable polymer compositions which are suitable for fabricating hard contact lenses.
The prior art known to us consists of the copolymers and articles of manufacture described in U.S. Pat. No. 3,808,178 to Gaylord. The copolymers described in the Gaylord patent are copolymers of polysiloxanyl acrylic esters and an alkyl acrylic ester. Gaylord also discloses that other comonomers can be employed to improve certain physical properties of his copolymers, such as acrylic or methacrylic acid to improve the wettability of the copolymer, and ethylene glycol dimethacrylate to improve the rigidity of the copolymer.
Tanaka, et al., U.S. Pat. No. 4,139,692 and Ichinohe, et al., U.S. Pat. No. 4,433,125 disclose soft contact lenses composed of hydrophilic moiety and polysiloxanyl propyl glycerol acrylate monomer having in one mole at least one group of the general formula: ##STR4##
The compounds of Tanaka and Ichinohe are practically identical to each other. The lenses formed from them are said to lie intermediate silicone rubber and conventional hydrophilic contact lenses in wettability and oxygen permeability, as shown in the U.S. Pat. No. 4,507,452.
Their monomers include in a molecule, a large group such as ##STR5## and its copolymers are liable to become soft. The larger amount of their monomer in a copolymer proportion increases to improve the oxygen permeability of the copolymer, the softer the copolymer becomes.
All of their monomers differ from the instant monomers in that their monomers are substituted on the alkylene chain with an hydroxyl substituent. There is no such substituent in instant monomers. Moreover, the carbon chain carrying the hydroxyl group in their monomers is three carbon atoms in length. In instant monomers it is only two carbon atoms in length.
Therefore, "4,139,692" and "4,433,125" do not teach the instant monomers much less the instant copolymers.
Deichert, et al., U.S. Pat. No. 4,153,641 disclose polysiloxane based polymers which are end capped with unsaturated groups which have polymerizable double or triple bond such as 2-cyanoacryloxy, acrylonitryl, acrylamide, acryloxy, methacryloxy, styryl, N-vinyl-2-pyrrolidone-3-yl, N-vinyl-2-pyrrolidone-4-yl and N-vinyl-2-pyrrolidone-5-yl. The Deichert poly(organosiloxane) monomer has the formula: ##STR6## wherein A is an activated unsaturated group, R is a divalent hydrocarbon radical, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are selected from the group consisting of a monovalent hydrocarbon radical or halogen substituted monovalent hydrocarbon radical, and m is 50 or greater.
The lenses made from his copolymers are soft contact lenses having a Shore hardness of 60 or below on the Shore hardness scale A.
U.S. Pat. No. 4,153,641 dose not teach the instant organolsiloxane monomers much less the instant copolymers.
Friends, U.S. Pat. No. 4,254,248 discloses monomeric polysiloxanes with a comonomer comprising a polycyclic ester of acrylic acid or methacrylic acid to form a soft contact lens having a Shore hardness of 60 or below on the Shore hardness scale A.
Therefore, the instant organosiloxane monomers and the instant copolymers are not taught in this article.
Ellis, U.S. Pat. No. 4,424,328 discloses hard contact lenses formed of unsaturated, multifunctional organosiloxane alone or mixed with monofunctional organosiloxane and alkyl acrylate and alkyl itaconate.
Ellis monomer has the formula: ##STR7## wherein Y' is an unsaturated polymerizable group, X' is a divalent hydrocarbon having from 0 to 10 carbons, Y is an unsaturated polymerizable group, X is a divalent hydrocarbon, A is selected from the group consisting of straight chain alkyl groups having 1 to 5 carbon atoms branched chain, or cyclic alkyl groups having 3 to 5 carbon atoms, phenyl groups and "Z" groups, "Z" is a group selected from the class consisting of trimethyl siloxy, pentamethyl disiloxanyl, heptamethyl trisiloxanyl, etc., "a" is an integer from 0 to 10, the total of "a" values is at least 2, "n" is an integer from 0 to 10, and each of said X, X', Y, Y', a, A and Z groups each individually being the same or different.
Foley, U.S. Pat. No. 4,507,452 discloses multifunctional silicon hydride comonomer which has the structural formula ##STR8## wherein n is a positive integer from 1 to 6, R is hydrogen, methyl or ethyl radical, and R' is hydrogen, or a monovalent hydrocarbon radical free of aliphatic unsaturation, typically methyl, ethyl or phenyl radicals, including substituted phenyl radicals, at least one R' being hydrogen radical.
His monomer is also generally similar to the Ellis monomer but having a silicon hydride group in a molecule.
There is neither disclosure nor suggestion of instant organosiloxane monomers having in a molecule at least one group of the structural formula ##STR9## wherein R1 is hydrogen or methyl radical, in the Ellis patent and the Foley patent.
Generally, copolymers formed from monomers containing siloxane bond are hydrophobic, and such copolymers can not be employed as materials of contact lens unless the monomers are copolymerized with wetting agents such as methacrylic acid. However, the copolymers formed by copolymerization of organosiloxane monomers and wetting agents are liable to become opaque. This is a fatal defect in use as a material of contact lens. Therefore, the proportion of organosiloxane monomers to wetting agents is limited for producing transparent copolymer. It is necessary to increase the amount of the organosiloxane monomers for obtaining the oxygen permeability enough to make the extended duration wearing capabilities. However, the more the amount of the organosiloxane monomers increases, the more hydrophobic the copolymers become. For this reason, a larger amount of the wetting agents must be copolymerized. When a large amount of the wetting agents is employed, the produced copolymer becomes opaque. In order to form a transparent copolymer, the amount of organosiloxane monomers and/or wetting agents must be decreased, and a copolymer having sufficient oxygen permeability, good wettability and transparency can not be obtained.
In contrast, instant organosiloxane monomers have one ether bond in a molecule and therefore, are miscible with wetting agents in all proportions and also a transparent copolymer can be obtained by copolymerization with a large amount of instant organosiloxane monomers and a large amount of wetting agents. The instant copolymers are colorless, transparent and hydrophilic, and have sufficient oxygen permeability.